Redry veneer drying method and apparatus



United States Patent O 3,434,221 REDRY VENEER DRYING METHOD AND APPARATUS Albert S. Hammond, Tacoma, Wash., assgnor to Weyerhaeuser Company, Tacoma, Wash., a corporation of Washington Filed Apr. 13, 1967, Ser. No. 630,567 Int. Cl. F26b 7/00 U.S. Cl. 34-6 4 Claims ABSTRACT OF THE DISCLOSURE A method and apparatus for drying wood veneer which does not become adequately dry when passed through drying zones and is therefore termed redry veneer. The method utilizes gaps which develop in the drying zones between portions of rst pass veneer, due to shrinkages and temporary stoppages in supply, by feeding the redry veneer into these gaps to be conveyed through less than all of the drying zones at normal speeds for rst pass veneer. The apparatus includes means to feed redry veneer into an intermediate point between drying zones.

CROSS REFERENCES TO RELATED APPLICATIONS This application relates to a process and apparatus useful in increasing the utilization of the drying and sorting equipment shown in the U.S. Patent No. 3,280,866 to Harold E. Erickson.

The reverse pass drying system disclosed in U.S. patent application 626,154, led Mar. 27, 1967, in the name of Conant Dodge, having a common assignee with the instant application, is particularly well suited for utilization of the apparatus and method of the instant application.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to the production of wood veneers and in particular to an improved process and apparatus for drying redry veneer in veneer production installations utilizing multiple drying zones.

Description of the prior art It is customary in the operation of the dryers for reducing the moisture content of Wood veneers that the drying conditions and conveying speeds used are those which will produce the maximum amount of satisfactorily dried veneer without producing unusable veneer due to overdrying. A good disclosure concerning the wide varia- -tion in input moisture content of veneer is that made in the U.S. Patent No. 3,199,213 to F. H. Milligan et al. In Schedule II thereof, a moisture content range for Douglas fir intermixed sap and heartwood veneer is between 150% and 27%. Milligan et al. teaches a process of raising the moisture content to the desired equilibrium moisture content of about after reducing the moisture content below this amount.

A more common practice is to set the dryer zone conditions and conveying speed so that the majority of veneer passing through the drying Zones will exit with an acceptable moisture content with little or no veneer being overdried. The remaining veneer, referred to as redry veneer, is unsuitable for immediate use as plywood components because it has too high a moisture content. It is considered normal practice to set the drying conditions and conveying speeds to yield about 5 to 20% redry Veneer.

In conventional plants the redry veneer is stored until enough is assembled to be passed through the same dry- ICC ing zones or to another dryer installation. In either situation the drying zone conditions and conveying speeds are specifically set to yield usable, properly dried veneer from the redry veneer input.

An example of the problem caused by the redry veneer additional drying requirement can be illustrated with reference to one of the most modern veneer production systems available as disclosed in the U.S. Patent No. 3,280,866 to Harold E. Erickson. The green or wet veneer 18 is fed into either the upper 66 or lower 68 dryer conveyor runs to pass through the two drying chambers. If some of the equipment on the lathe side of the dryer (the green end) breaks down, it is possible to feed the redry veneer into the dryer at the upper 54 or lower 37 redry feeders. However, to avoid overdrying the redry veneer, it has been necessary to empty the dryer of regular veneer, which takes about ten minutes, and then double the conveyor speed for transporting the redry veneer through the dryer. After the green end breakdown is repaired, it has been necessary to empty the redry veneer, which takes about five minutes, before the conveyor speed can be reduced for proper drying of vgreen veneer. The same magnitude of time loss d-uring the emptying period for making the transition from drying green veneer to drying redry veneer and back is experienced in the use of the reverse pass drying system disclosed in the above referred to application of Conant Dodge.

SUMMARY OF THE INVENTION Applicant has developed a method of drying redry veneer wherein the lost time, caused by changing conveying speeds to accommodate a change from drying green veneer to redry veneer and back, is eliminated. Applicant provides means to feed or oifbear redry veneer into or out of an intermediate station between drying zones so that the redry veneer can be conveyed through the dryers at the same speed as the green veneer without overdrying, Since the redry veneer does not transit the full length of the path transited by the green Veneer. Any gaps between edges of green veneer pieces as they transit the intermediate station between two drying zones may be filled by redry veneer yfed into the drying line at4 the intermediate station.

Other related features of the invention will become more fully apparent as the following description is read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIGURE l is a side elevation view of the general arrangement of the rst embodiment of the in-line veneer drying system, including redry veneer conveying equipment in accordance with the instant invention;

FIGURE 2 is a schematic drawing showing the path of the normal green and redry veneer as its passes through the equipment as shown in FIGURE 1 in accordance with the method of the instant invention;

FIGURE 3 is a side elevation View showing the general arrangement of a second embodiment of the veneer drying system useful in a reverse pass dryer installation in accordance with the instant invention; and

FIGURE 4 is a schematic drawing showing the path of the normal green and redry veneer as it passes through the veneer drying system as shown in FIGURE 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings with more detail, the rst embodiment of the improved veneer drying system 1 is shown in FIGURE 1. Following the path of the veneer from left to right, the system 1 includes a normal green veneer dryer feed station 5, a first drying chamber 18, an intermediate transfer station 28, a second drying cham ber 36, a sizing station 45, and a sorting station 52.

Accumulated green veneer 2 is fed into the first drying chamber 18 at the dryer feed station 5 by means of the upper or lower feed tipples 6 or '7, across the upper or lower feeder transport conveyors 10 or 11, along the upper or lower feeder carrying conveyors 12 or 13, being held down by the upper or lower feeder hold-down conveyors 14 or 15.

The first drying chamber 18 may include a series of individual dryer sections having different conditions of temperature and air velocity. To simplify the explanation of the essence of this embodiment, it is adequate to consider the establishment of an upper drying zone 24 as that through which the veneer passes as it is held by the upper dryer carrying conveyor and held down by the upper dryer hold-down cables 22. In a like manner, a lower drying zone 25 is established in the path of the veneer as it is carried through the first drying chamber 18 supported by lower dryer carrying conveyor 21 and held down by lower dryer hold-down cables 23.

In the normal transit of the green veneer, it would pass from the first drying chamber 18 through the intermediate transfer station 28 to the second drying chamber 36. As shown, an upper drying zone 42 is established in the second dryer chamber 36 in the path transited by the veneer as it is conveyed on the upper dryer carrying conveyor 38 and held down by the upper dryer hold-down cables 40. In a similar manner, a lower drying zone 43 is established in the second drying chamber 36 in the path transited by the veneer as it is conveyed along the lower dryer carrying conveyor 39 and held down by the lower dryer holddown cables 41.

As the veneer exits from the end of the upper drying zone 42 and out of the second drying chamber 36, it is conveyed along upper feed conveyor 46 to be sensed for moisture content by upper moisture meter 48 and sized by upper sizing clipper 50 prior to being conveyed to the upper sorting table 54. As the veneer is conveyed through the lower drying zone 43 and exits from the second drying chamber 36, it passes through lower moisture meter 49, where its moisture content is sensed. It is then clipped to size by lower sizing clipper 51 and transported to the sorting station 52. The sized veneer is supported by the upper and lower sorting tables 54 and 55 and divided into stacks by a sorting crew which separates the useful veneer 56 from the redry veneer 57.

With reference to FIGURES 1 and 2, it is seen that the normal path of the green veneer is from the dryer feed station 5, through the drying zones 24 or 25 in the first drying chamber 18, then through the intermediate transfer station 28, into and through drying zones 42 or 43 established in the second drying chamber 36, and finally through the sizing station 45, to the sorting station 52. There are two paths available for the redry veneer 57. The first, as shown in FIGURE 2, is from the sorting station 52, back the full length of the rst and second drying chambers 18 and 36, to the upper or lower redry loaders 8 and 9, where the stored redry veneer 3 is accumulated prior to feeding it onto the upper or lower feeder transport conveyors 18 or 11. The redry veneer then passes through drying zones 24 or 25 in the first drying chamber 18 and reaches the intermediate transfer station 28. At this point the redry veneer is taken out of the line by means of upper or lower convertible transfer conveyors or 31, so termed since they may operate as either offbearing conveyors, to remove the redry veneer from the upper or lower dryer carrying conveyors 20 or 21, or as infeed conveyors, to feed veneer onto the upper or lower dryer carrying conveyors 38 or 39. The second path for the redry veneer, as shown in FIGURE 2, is from the sorting table 52, back to the intermediate transfer station 28, where it is stored as assembled redry veneer 29 to be ted into the second drying chamber 3 6 by means of the upper or lower convertible transfer conveyors 30 or 31.

It is seen that the operation of the first embodiment 1, as shown in FIGURES l and 2, provides many desirable results. By providing convertible transfer conveyors 30 and 31 at the intermediate transfer station 28 between the first and second drying chambers 18 and 36, it is possible to feed redry veneer into any gaps which might occur between the edges of green veneer fed into the first drying chamber 18. Such gaps may exist for a variety of reasons. One reason is the lack of an adequate supply of green veneer at the dryer feed station 5. It is also possible that for some species of wood the drying medium conditions in the first drying chamber 18 would cause enough shrinkage of the veneer pieces as they transit from one end of the rst drying chamber 18 to the intermediate transfer station 28 to provide an adequate space for feeding between individual pieces of green veneer a piece of redry veneer. Recent experience, however, has been to the contrary with regard to the significance of the shrinkage, in that of a total shrinkage of approximately 5% for the full transit of the veneer from the dryer feed station 5 to the sizing station 45, there was only a 0.6% shrinkage in the veneer by the time it reached the intermediate transfer station 28. The third, and probably the most common, cause for gaps developing between the edges of adjacent green veneer pieces is that of machine breakdown or stoppage of equipment on the lathe side of the dryer feed station 5. In prior practice the dryer gaps produced during short duration stoppages of the lathe, for minor adjustments or removal of nicks from the lathe knife, ywere not used. With applicants equipment redry veneer is fed into these gaps.

With reference now to FIGURES 3 and 4, the second embodiment 60 is shown, which includes, in the normal path of green veneer, accumulated veneer storage trays 64 which feed the accumulated green veneer 65, across feeding tipple 67, into drying chamber 70. As the veneer transits from left to right through the drying chamber 70, it is carried on upper carrying cables 74 and held down by upper hold-down cables 72. It exits from the drying chamber 70 into the turn-around transfer station 80, where its direction is reversed. The veneer is then fed back through the drying chamber 70 by lower carrying cables 75 being held down by lower hold-down cables 74. As the veneer exits from the left end of the drying chamber 70, it is conveyed by means of cooling transport conveyors 92 through a cooling chamber 90 up to a sizing station 94, Where it passes a moisture meter 95 and is clipped by sizing clipper 96 before it is conveyed t0 sorting table 97. The first drying zone of the drying chamber 70 is the upper drying zone 76 established between the upper carrying cable 74 and upper hold-down cable 72. The second drying zone is the lower drying zone 77, which is established between the lower carrying cable 75 and the lower hold-down cable 74.

In operation, with reference to FIGURES 3 and 4, the normal path for the green veneer is first from left to right through drying zone 76, reversing direction at the tum-around transfer station 80, coming back through the drying chamber 70 into the second lower drying zone 77, from where it is conveyed to the sorting table 97. At the sorting table 97, the useful veneer 98 is separated from the redry veneer 99. The redry veneer 99 is then conveyed back to the turn-around transfer station 80. As shown, the stored redry veneer 83 is supported on a redry feeder 87 positioned at the tum-around sta-tion 80. As gaps develop between the edges of normal green veneer as it exits from the upper drying zone 76 and passes into the turn-around transfer station 80, the redry Veneer is placed between these gaps so that it passes down into the lower drying zone 77 and is again conveyed back to the sorting table 97. It, of course, would be possible to use a convertible transfer conveyor in place of the redry feeder 87, so that redry venneer could be fed into the upper drying zone 76 from feeding tipple 67 to be otfborne from the drying line at the turn-around station 80.

It is therefore seen that I have disclosed a generally improved method and apparatus for drying redry veneer by inserting it into the gaps, which are otherwise unused, as they exist between individual pieces of veneer passing through the drying zones. By combining the redry feeding and oibearing apparatus with the drying chamber conveyors at the transfer stations, it has been possible to use less than all of the drying zones for drying the redry veneer and thereby eliminate the time lost due to changing the speed of the drying conveyors to keep from overdrying the redry veneer.

What is claimed is:

1. In a process for drying green veneer to a maximum moisture content by conveying said green veneer through a minimum of two drying zones at a standard range of speeds required to adequately dry the majori-ty of green veneer conveyed through said zones,

sensing the moisture content of said green veneer,

separating said green veneer into dry veneer having a moisture content not greater than said Vmaximum moisture content -and redry veneer having -a moisture content greater than said maximum moisture content, and

conveying said redry veneer through additional drying zones until its moisture content is not greater than said maximum moisture content,

the improvement comprising:

interspersing said redry veneer into gaps formed between individu-al strips of green veneer, and

conveying said redry veneer through less than al1 of said first drying zones at said standard range of speeds.

2. The process of claim 1 wherein the green veneer is conveyed through one drying zone in one direction and 6 reverses its direction at a turn-around station to be conveyed through another drying zone in the opposite direction, the improvement comprising:

introducing said redry veneer in the path of said green veneer at said turn-around station. 3. In an apparatus for the production of dried wood veneers:

tirst means for transporting veneer through a first drying zone ina first direction; second means for transporting said veneer through a second drying zone in a second direction opposite said first direction; transfer means positioned between said lirst and second means for conveying said veneer from said rst means to said second means, including turnaround means for changing the direction of travel of said veneer from said rst to said second direction; and veneer feeding means positioned between said transfer means and one of said zones for introducing veneer into said second means. 4. The apparatus of claim 3 wherein: one of said transport means is over the other of said transport means, and said veneer feeding means is between said upper transport means and said transfer means.

References Cited UNITED STATES PATENTS JOHN I. CAMBY, Primary Examiner.

U.S. C1. X.R. 

